Cross-range wind (crosswind) compensation is part of most precision long-range gunnery. Snipers do it by estimation, training and experience. It is done in tank gunnery, using only the locally measured crosswind speed at the tank. Artillery may use meteorological data for the high altitude winds between battery and target. Crosswind measurement is applicable to any direct-fire projectile and to many indirect-fire weapons as well. The most challenging of these crosswind compensations is the long range sniper scenario. The sniper fires a small projectile (bullet) a long distance through unknown and varied low-level winds. Thus, the sniper scenario is one of the more sensitive cases of cross-range compensation.
Traditionally snipers estimate crosswind based on environmental cues such as grass movements or visible “mirage.” These methods rely partially upon instincts and are imprecise and difficult to master. Nevertheless, highly trained snipers use these methods to achieve astonishingly accurate results at times. For instance, in 2004 a world record was set in which six sets of five shots each landed inside a 16 cm circle at 1000 yards. During the afternoon event that same day, however, the same shooter entirely missed the 6′ square target 7 of 10 shots before being eliminated from contention.
It is known that the path of a projectile fired from a sniper's rifle (e.g., a bullet fired from a rifle) will be adversely affected by any crosswinds existing between the firearm and the desired target. For example, a crosswind having a horizontal component orthogonal to the line of sight between the weapon and the target will deflect the projectile to the left or right of the target. Depending on such factors as the magnitude of the horizontal (or vertical) crosswind component, the distance between the firearm and the target, and the size of the target, mass of the projectile, a crosswind may result in an otherwise properly aimed projectile missing the target entirely. Hence, crosswinds present a significant challenge in situations calling for precise targeting, particularly over long distances.
Indirect methods such as Doppler triangulation or dynamic speckle statistics have operational drawbacks due to large footprints, large apparatuses, or long data collection times. Moreover, such conventional methods are not able to adequately account for a non-homogeneous crosswind, i.e., a crosswind having a magnitude that varies along the distance between the firearm and the target. In addition, conventional methods are prone to inaccuracies occasioned by motion and/or vibration of the measuring device. Some examples of approaches that attempt to gauge cross-range wind include: eye-balling a target with instincts and training 102, FIG. 1; laser Doppler velocimeter (LDV) that only measures tailwinds 104, FIG. 1; LDV parallax that is able to determine cross-range wind compensation, but is restricted to wide-open spaces and requires cumbersome equipment 106, FIG. 1; scintillation correction may work in homogeneous wind applications, but is less efficient in non-homogeneous wind 108, FIG. 1; and instrumented range which is impractical in real world applications because anemometers are placed at multiple points (i.e. every 50 meters) between the weapon and the target 110, FIG. 1.
None of these approaches solves the problems of cross-range wind compensation. It would be therefore be advantageous to be able to easily measure the crosswind between a weapon and its intended target and then be able to adjust the aimpoint of the weapon by an offset amount that accounts for the measured crosswind.
In view of the foregoing, the present disclosure provides a novel approach to determining the crosswind as a function of downrange distance that does not have the drawbacks of previous attempts.